Upgrading Shimano road hydraulic disc to DI2 - can I use existing calipers (RS785)?

[Ross]

Do I just need the shifters (and obviously the Di2 cables etc)? Are the existing brake lines/hoses compatible?
Currently running Shimano post mount BR-RS785 Hydraulic Disc, 160mm Rotors, Shifters Shimano RS685 22-Speed

[NewStew]

Cant be 100% sure since I am not a qualified mechanic but I have exactly those brakes running with the earlier non-series ST-R785 Di2 shifters on my bike so I am pretty sure it should work like a dream. Now whether you can pair them with the newer 8070 and 9070 Ultegra and Dura Ace series levers I dont know but I suspect they will be fine too.

[Ross]

I was looking at a second hand set of levers and calipers but the caliper on offer are flat mount and I need post mount and so if I already have PM calipers I won't need them anyway. But...depending on if the guy selling wants to sell me just the shifters and for how much. New RS785 shifters only are about $600 but it looks like I can buy new shifters and calipers and presumably brake lines for under $500...go figure. Waiting for shop to email me back confirm this is the case.

Or...I could just continue to ride with what I have...but where's the fun in that?!

[MichaelB]

From my experience, yes.

You should just be able to reconnect and bleed. No idea re the Di2 side though

[Patt0]

I seem to recall there being two types of hose connectors. Best to make sure what you have and what you get are compatible.

[Duck!]

Completely compatible.

[Ross]

What about this hose business, Duck?

[MichaelB]

What about this hose business, Duck?

As he said, completely compatible.

As a learning exercise, I'd get au fait with the Shimano Tech Docs, especially the exploded views (EV suffixes), as that will answer just about everything, and if you do need something, you just do a google for the shimano part number.

They are a really handy resource

[Duck!]

What about this hose business, Duck?

Shimano do have two different hoses, used for both road and MTB brakes; "standard" BH59 and "high power" BH90. The BH90 hose has a thicker wall and correspondingly smaller internal bore diameter, but the same external diameter as the BH59. The barbed insert is correspondingly smaller, but the olive and compression nut are common to both hoses. Officially, certain brake models are suggested to be used with a particular hose, as much a part of the difference between groupset levels as anything else, but there is no fundamental incompatibility.

[Duck!]

I seem to recall there being two types of hose connectors. Best to make sure what you have and what you get are compatible.

The different hose fittings are for the caliper end, not the lever end. Not a concern when only swapping levers.

In the scenario presented by the OP, the solution is to simply disconnect the existing RS685 levers from the hoses, swap in the new levers leaving the existing hoses & calipers in place, and bleed to fill the reservoirs.

For what it's worth though, all the flat-mount calipers and the RS785 post-mount use the straight hose fitting; only the original R785 used the banjo fitting.

[Jmuzz]

Someone on Facebook Bicycle Market had a let of Di2 levers and calipers up.